1. Field of the Invention
This invention relates to methods of and apparatus for editing a digital audio signal recorded on a record medium in association with a video signal.
2. Description of the Prior Art
Years ago, the editing of an analog audio signal recorded in a longitudinal track on a video magnetic tape wound on open reels, and having the associated video signal recorded in oblique tracks on the tape, was done by rocking the tape to and fro by manually rotating the reels, while listening to the reproduced audio signal. In this way, the gap between words or between effects noises could be found, and the tape marked with a chinagraph pencil.
More recently this crude method has given way to a method where the tape movement is controlled by a jog knob. Moreover if the video signal recorded in association with the audio signal has a vertical interval time code (VITC), the VITC can be read even from a stationary tape to identify precise time positions for accurate and repeatable cueing and synchronization.
The problem now arises with modern digital video tape recorders (DVTRs), that the audio channels, which are recorded as digital data blocks at the beginning and/or the end and/or an intermediate position of each oblique track on the tape, cannot be read at non-play or jog speeds.
To overcome this problem, it has been proposed to use the audio signal recorded in the longitudinal analog tracks on the tape, the tape being moved under control of the jog knob to find the edit points. However, this solution is inapplicable where the audio signal to be edited only exists in the digital channels in the oblique tracks. Moreover, the operation of the job knob may not feel right to the operator, leading to slow operation and errors. This is because pulses generated on movement of the job knob are supplied via a microprocessor to control a tape transport servo. Depending on the time delays involved and the torque of the servo, the operation can feel spongy and imprecise, leading to difficulty in locating edit points accurately.